1. Field
The subject matter disclosed herein relates to electronic devices, and more particularly to methods and apparatuses for use in providing expected signal data to a mobile station.
2. Information
The Global Positioning System (GPS) and other like satellite positioning systems have enabled navigation services for mobile handsets in outdoor environments. Since satellite signals may not be always be reliably received and/or acquired in an indoor environment, different techniques may be employed to enable position estimation and related navigation services. For example, mobile stations can typically obtain a position fix by measuring ranges to three or more terrestrial radio transmitters which are positioned at known locations. Such ranges may be measured, for example, by obtaining a MAC ID address from signals received from such access points and measuring one or more characteristics of signals received from such access points such as, for example, signal strength, round trip delay, just to name a few examples.
By way of additional example, a mobile station, such as, a mobile phone, smart phone, etc., may perform signal-based position estimation to identify its location within a structure by taking measurements, for example of a signal strength (e.g., an RSSI) and/or propagation time (e.g., a round-trip time (RTT)) for signals exchanged with various radio transmitters (e.g., access points, beacons, etc.). A mobile station may use these or other like measurements to obtain a probability distribution over a region of space (e.g., defined using two or coordinates (x, y), etc.). Such a probability distribution or other like information may, for example, be used in a particle filter, Kalman filter, and/or other positioning mechanism using known techniques.
To support such a process, expected signal data, such as, may be related to a “heat map”, “radio map”, and/or other like form of information, may be used for probability lookup. In an example, expected signal data may take the form of a table listing an expected mean and standard deviation of a signal measurement quantity for each identifiable position point (e.g., (x,y) positions, etc.). With such information, a mobile station may convert signal measurements to a probability value for selected candidate position points.
Expected signal data may be provided to a mobile station by one or more remote devices. In certain instances, such as, for a large building or other complex structure, there may be a significant amount of expected signal data to transfer to a mobile station. Consider, for example, a uniformly distributed grid of position points set one meter apart, covering a one hundred meter by one hundred meter floor of a shopping mall. Here, there would be ten thousand position points, for which expected signal data would be provided for each radio transmitter that may support the position estimation capability of the mobile station. Further still, for example, for each position point a mean value and a variation value (e.g., a standard deviation) may be provided. Thus, assuming that such values are represented by one byte of data, in this example the expected signal data for sixteen radio transmitters would take about 320 kB. Moreover, such example shopping mall may have additional floors. Transmitting such a large amount of data from a network to a mobile station may prove costly in terms of power, bandwidth, and latency. Additionally, such expected signal data would also consume a significant amount of memory on the mobile station.